The Primary objective of this Phase 1 dose-escalating study of recombinant human interleukin-12 (rhIL-12) is: 1) to assess the safety and maximum tolerated dose of rhIL-12 when administered by intravenous injection in patients with advanced malignancies. The secondary objectives are: 1) to evaluate the serum concentrations of rhIL-12; 2) to determine the immunopharmacology profile of rhIL-12; and 3) to explore the efficacy of the dosing schedule and route of administration.